Railroad transport, involving a string of attached railroad cars moving along a track, is used to transport passengers and a variety of cargos throughout the world. Railroad cars designed for carrying cargo are generally referred to as freight cars. Different freight car designs have been developed to more effectively meet the specific needs of different types of cargo. Examples of some different types of freight cars include boxcars, flatbed cars, tank cars, hopper cars and gondola cars. Freight trains may include many freight cars connected together, end-to-end in a long line. A freight train may be dedicated to a single typical cargo, in which case all or most of freight cars may be of a similar design, or a single freight train may haul a variety of different types of cargos, in which case it may be comprised of many different freight car designs to accommodate the different types of cargo.
Coal and other mineral commodities are often transported in dedicated freight trains, and especially when being transported from a mine. Such mined commodities are examples of bulk materials, or bulk commodities, and more particularly dry bulk commodities or dry bulk materials, which are typically loaded into freight cars in bulk form. Some examples of bulk materials include grains, ores, minerals, coal, food products, building materials, or any other material suitable for transport in a bulk fashion.
Many bulk commodities of a particulate nature, such as coal, mineral products and grains are often transported in top-loading freight cars, examples of which are gondola cars and hopper cars. For many bulk commodities, including coal, the freight cars are generally open at the top for most or all of the entire length of the freight car, which permits convenient loading of the entire freight-containment volume of the freight car from above while the freight car is moving. Transport in such open-top freight cars is efficient and convenient, and a significant infrastructure has been developed to handle loading and unloading of the large volume of bulk materials transported in such open-top freight cars.
Loading of bulk commodities into an open-top freight car is often accomplished by discharging the bulk material into the freight-containment volume from above via a loading chute positioned above or within the freight-containment volume of the freight car. Loading often occurs while the freight car is moving (rolling along the tracks in relation to the chute, so that bulk material is loaded along the entire length of the freight car). Unloading an open-top freight car is often accomplished either by a “bottom dump” or a “rotary dump” operation, depending upon the design of the freight car. In a bottom dump unloading operation, the bulk material is discharged from the bottom of the freight car, such as through chutes or doors located at the bottom of the freight-containment volume of the freight car. This may be the case, for example, for an open-top hopper car. In a rotary dump unloading operation, the entire freight car is rotated to the side until the bulk material spills out of the freight-containment volume. During the operation, the freight car is held in place on a rotating platform or other rotating structure, such as through the use of retaining clamps that are clamped pressed to the walls of the freight car. A structure surrounding the clamp and freight car is provided in order to pivotally rotate the rail car about a longitudinal access such that the freight car is transferred from an upright position to one where the freight car is on its side, or even upside down, such that the bulk material flows, or spills, out of the open top of the freight car. The freight cars may be connected together with rotary couplings to permit the rotation of one of the freight cars at a time or a few of the freight cars as a unit.
As will be appreciated, loading and unloading infrastructure is based on there being a level of uniformity in design among open-top freight cars.